A code division multiple access (CDMA) communication system may include a base station and a number of mobile stations. The base stations adjust power levels of a number of communication channel signals targeted for a corresponding number of mobile stations and at least a control channel signal, and code-multiplexes the signals to produce a combined signal. The base station transmits the combined signal via a wireless communication downlink from the base stations to the mobile stations.
When a mobile station receives the combined signal, it code-demultiplexes the received combined signal according to its assigned multiplexing code to recover its targeted communication channel information. The mobile station measures a signal-to-interference ratio of the code-demultiplexed control channel signal or communication channel signal or both, and compares the result to a power control threshold to produce a power control data bit. The mobile station transmits the power control data bit to the base station via a wireless communication uplink. The base station adjusts the power level of the communication channel signal targeted for the mobile station according to the status of the power control data bit.
The level of the power control threshold is independently determined such that when the signal-to-interference ratio of the received signal is at a level comparable to the threshold, the signal may be demodulated at an adequate frame error rate in the receiver section of the mobile station. The level of the power control threshold is dependent on the level of the adequate frame error rate as determined by the communication system standard. The power level of the communication channel signal is adjusted to account for channel variations such that an adequate frame error rate is maintained. Furthermore, the power level of the communication channel signal is adjusted to maintain a comparable power levels among all mobile stations in the communication system.
Similarly, the base station also compares the signal-to-interference ratio of a signal transmitted from the mobile station in the uplink to a power control threshold. A power level control data bit as a result of the comparison is transmitted to the mobile station in a downlink traffic channel to change the mobile station transmit power level. If the signal-to-interference ratio is less than the threshold, power control data bit indicates an increase of power level, and if conversely, it indicates a power level decrease.
In the prior art, communication channels have been of the same type such as a voice channel type. Therefore, a power control data bit and a power control threshold have been sufficient to control power level of each channel signal to maintain an adequate communication link. Recently, various telecommunication standard committees have proposed a CDMA communication system that provides a number of communication type services simultaneously. Such a system is commonly know as the 3G-CDMA system. In the proposed CDMA communication system, voice, video and data channel types signals are code-multiplexed, or code and time multiplexed to produce a combined signal. Documents regarding such proposed communication systems and other information may be obtained by contacting European Telecommunication Standard Institute (ETSI), located European Telecommunications Standards Institute, 650 Rt. des Lucioles-Sophia Antipolis, Valbonne-FRANCE. The combined signal may be transmitted from a mobile station on an uplink or from a base station on a downlink. The mobile station and the base station simultaneously in a single connection communicate voice, video and data information. Normally, a communication channel of voice type signal has a frame error rate requirement that is different than frame error rates of other types of communication channels, such as video and data types. As a result, a common power control data bit and a common power control threshold are not sufficient to control power level of all channel types signals to maintain an adequate communication link for services of all channel types.
Therefore, there is a need for a power control scheme that solves the problem of satisfying different requirements of communicating signals of various channel types.